Anyone who has watched a spy film knows that secret messages are often sent between agents using invisible pen. It’s a fun way to pass along a note without being noticed, and it’s even possible for kids to create their own invisible ink. You only need a few household items, a UV or black light and a few other common household items to reveal the message.
During World War II, the SOE used invisible ink to communicate between agents operating behind enemy lines. They identified the properties of an ideal invisible ink: Must mix easily with water and should not leave a noticeable smell or deposit crystals on the paper. Must not be heated (as with lemon juice) or react to other chemicals such as iodine. It should not also stain the paper.
Inks that glow when exposed to UV light, specially formulated inks, are used widely. They’re especially useful for marking products during manufacturing and for tickets for events. They’re even used in some passport photos to make tiny yellow dots that only appear when viewed through a certain type of camera.
Poker cheating sunglasses, or gambling glasses, are a type of sunglasses that allow a player to see invisible ink marks on the backs of marked cards. These sunglasses are not like other invisible ink devices such as poker analyzers. They look like regular sunglasses, so other players won’t recognize them as cheating devices. These sunglasses can also be customized to suit your preferences, so you can select them according to the environment in which you play.